One-time mission plan: At,batch
Recurring Task Scheduler: Cron
At: Simple usage
At time
At>
Submit Task: ^c+d
Job Result: Send the current user on the system as a message
Send and receive mail:
Service start or Not Status View command:
NETSTAT-TNL |grep ": 25"
The default send and receive messages are only made between users on this computer and only through addresses on the loopback interface.
# Mail
Q: Exit
N: View Nth message
Send an email to the specified user (within the system):
# Mail username[@HOSTNAME]
-S "SUBJECT" theme
echo | Mail can also use pipelines
Format of Time
Exact time:
hh:mm
Blur Time:
now+ #UNIT
Noon, Midnight,teatime, tomorrow
Job Queue view:
At-l, ATQ
To delete a job that has not been run:
at-d [Job_num], at RM
You can also put all the tasks at the at to be executed in the file so that at reads this file as the task to be run (for a large amount of jobs)
At-f/path/to/somefile Time
Batch: No time is required and will automatically run at a later point in time for a system resource that is idle
Recurring Task Scheduler: Cron
Rely on background services to view the running status
Service Crond status CentOS {5,6} version view command, you can use cron if you have the following output
Crond (PID 1680) is running
There are two types of cron tasks:
System cron:/etc/crontab
User cron: Defined in a file with the same name as the user name in the/var/spool/cron/directory
Each row defines a separate task:
The following information is available after viewing/etc/crontab
[Email protected] ~]# Cat/etc/crontab
Shell=/bin/bash
Path=/sbin:/bin:/usr/sbin:/usr/bin
Mailto=root
# for details see Mans 4 Crontabs
# Example of Job definition:
#.----------------Minute (0-59)
# | .-------------Hour (0-23)
# | | .----------Day of Month (1-31)
# | | | .-------month (1-12) OR jan,feb,mar,apr ...
# | | | | .----Day of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * * user-name command to be executed
Consists of the following 3 parts:
Point in time (recurring task)
User-name: User Identity
Command: The task to run
Note: It is recommended that when you define a cron task, the command you use uses an absolute path, or a custom environment variable that has a full path.
Time notation:
1. Each time is a value in the range of valid values that should be used for the period, * to represent all valid values for the period of use,
2. */#: At the corresponding time bit valid value on every # time unit once
Note: The range of values defined for a minute should be divisible by 60
3. Continuous point of time:-
4. Discrete point-in-time:,
Results after the task is run: The message is sent to the task-related user:
Drop message notification: output redirection
COMMAND >/dev/null
COMMAND &>/dev/null
COMMAND >/dev/null 2>&1
/dev/null: Software-simulated device, bit bucket, data black hole
Definition of User cron task:
crontab command:
-L: Lists all tasks that have been defined
-E: Open editor
-r:remove, remove All Tasks
-u User: Not managing your own cron task, but specifying the target user's cron task; root only has permissions to manage other users ' cron tasks; By default, manage your own
Note: The% in the crontab file must be escaped or referenced in single quotation marks.
Homework::
Every Monday to Saturday 3:20 A.M., run the CP command to save the/etc/directory for archiving, the storage location is/BACKUPS/ETC-YYYY-MM-DD
3 * * 1-6/bin/cp/etc/backups/etc-$ (date+ '%y-%m-%d ')
[[email protected] ~]# mkdir-p/backups/etc[[email protected] ~]# crontab e[[email protected] etc]# CRONTAB-L20 3 * * 1- 6/bin/cp/etc/backups/etc-$ (date + '%y-%m-%d ')
Every Sunday 2:30 A.M., run the CP command to back up the/etc/fstab file with a storage location of/BACKUP/FSTAB-YYYY-MM-DD-HH-MM-SS
2 * * 7/bin/cp/etc/fstab/backup/fstab-$ (date + '%y-%m-%d-%h-%m-%s ')
[[email protected] etc]# mkdir-p/backups/fstab[[email protected] etc]# crontab e[[email protected] etc]# crontab L30 2 * * 7/bin/cp/etc/fstab/backup/fstab-$ (date + '%y-%m-%d-%h-%m-%s ')
Every night 12 o'clock, get all lines in the/proc/meminfo file that begin with S or M, append to the/statistics/meminfo.txt file, and precede the daily message with a similar =============== separator line
6 0 * * */bin/egrep/proc/meminfo "^[s,m].*" >>/statistics/meminfo.txt && Echo ========================= = >>/statistics/meminfo.txt
[[email protected] etc]# mkdir-p/backups/fstab[[email protected] statistics]# crontab E[[email protected] statistics]# C RONTAB-L6 0 * * */bin/egrep/proc/meminfo "^[s,m].*" >>/statistics/meminfo.txt && Echo ================ ========== >>/statistics/meminfo.txt
A brief summary of Linux recurring Task Scheduler at and Cron